Response of biochar induced carbon mineralization priming effects to additional nitrogen in a sandy loam soil

• Nitrogen promoted the priming effects by biochar at early incubation stage.
• Nitrogen inhibited the priming effects by biochar at later incubation stage.
• N had no influence on native soil-derived dissolved organic carbon.
• N affected priming effects by biochar through change of soil microbial community.

The responses of soil carbon (C) mineralization priming effects induced by biochar to nitrogen (N) and the mechanisms in relation to soil microbial community and C availability were examined. A sandy loam soil (under a long-term C3 crop rotation) amended with biochar derived from maize straw (C4 crop) with or without additional N was incubated for 30 days. Primed native soil-derived carbon dioxide emission by biochar was −64.4 and −95.9 mg C kg−1 in soils without and with N, respectively; and additional N showed no influence on priming effects (−66.9% and −72.0%) during the whole incubation. Whereas, N increased (p < 0.05, n = 6) the magnitude of priming effects from −68.3% to −83.5% at the early incubation stage (days 0–11) while N decreased (p < 0.05, n = 6) that from −64.9% to −38.8% at the late incubation stage (days 11–30). Nitrogen increased microbial biomass (p  > 0.05, n = 6) and the proportion of gram-positive (G+) bacteria (p < 0.05, n = 6) while N decreased the ratios of gram-negative to G+ bacteria (p > 0.05, n = 6) and aerobic to anaerobic microbes (p < 0.05, n = 6) as estimated by phospholipids fatty acids at the beginning of the incubation. The opposite impact, however, occurred on day 11 in biochar-amended soils. On the other hand, N had no influence on native-soil derived dissolved organic carbon throughout the incubation in biochar-amended soils. Therefore, the results indicated that N could affect biochar induced C mineralization priming effects through the change of microbial community, especially the increase of G+ bacteria in the soil tested.